The Duggar women have wardrobe restrictions because of their religious beliefs, which is why the Duggars only wear skirts or dresses and never pants.
Dressing both modestly and femininely is a part of their family tradition, which is based heavily on their beliefs as independent Baptists. The girls in the family have opened up about this issue and claim that their modesty isn’t because of low self-esteem or being embarrassed of their bodies but because they view their bodies as a special gift from God that is intended to be shown only to their future husband. This is a form of religious-based purity similar to the abstinence pledge, which is also a way of saving one’s body for their future spouse. The women are expected to uphold these dress restrictions despite what might be considered appropriate for various activities like playing outdoors, biking, and horseback riding. This includes no shorts or tank tops whether male or female regardless of the time of year; the entire family practices these values of modest dressing and attempts to remain covered from the neck to below the knee.
The Duggar family also avoids public beaches and pools in order to keep the men from accidentally viewing other women who do not share the same dress restrictions and values. However, the family still goes to private pools and lakes but wears significantly more modest swimsuits than what’s popular and considered normal in the broader culture. Dressing modestly is only one aspect of their lifestyle that is dictated by their religious beliefs.